"I don't know where you could buy such a spacer, you might have to make it."
The angle of the wedge spacer would only have to be 2 or 3°. That's not much of an angle and it probably could be accommodated by the mounting screws without problem. For each degree you angle the cart, you save 5.3mm (?) arm height. It's much more efficient to angle the cart instead of at the end of 10.5" hypotenuse. You need a precisely made wedge that fits between the cart mounting screws and is approximately the length of the cart. If the cart hangs over the end of the headshell, subtract that amount from the length of the spacer.
neo